Lithographic techniques are well known in the art for forming precise circuit patterns on substrates in the fabrication of integrated circuits. Lithographic techniques have been used to form both positive and negative tone photoresist images. However, those skilled in the art generally prefer positive tone images because of processing advantages. For example, in electron beam direct write lithography, positive tone images generally require less writing. In optical lithography, most of the area of a positive tone mask will be composed of metal and therefore the mask will be less likely to be effected by opaque airborne contaminates which land on the mask during operation. Positive resists are also preferred in the fabrication of contact holes.
The diazonaphthoquinone/novalac positive tone, wet developed resist system is widely used in the industry. However, the wet development of the resist results in isotropic images which contribute to resolution problems especially with decreasing feature size.
In order to overcome the isotropic development problem, there is a desire to discover an effective dry developed positive tone resist system. Ito et al., U.S. Pat. No. 4,657,845 "Positive Tone Oxygen Plasma Developable Photoresist", issued Apr. 14, 1987, disclose a positive tone, dry developed resist system. The system involves the use of methyl isocyanate and is not widely used.
Ito et al., "Highly Sensitive Thermally Developable Resist System" J. Vac. Sci. Technol. B6(6) November/December 1988 p. 2259, disclose a bilayer, dry developed, positive tone resist system. Bilayer resist systems require additional processing steps resulting in increased process complexity and cost. Therefore, there is a continuing need in the art for a dry developed, positive tone resist system.
It is therefore an object of the present invention to provide a process for generating a positive tone, dry developed, resist image for use in making integrated circuits.
Other objects and advantages will become apparent from the following disclosure.